Ceramic matrix composite component with modified thermal expansion and method for producing the same

ABSTRACT

A ceramic matrix composite (CMC) material component is provided that includes a CMC material and an environmental barrier coating (EBC). The CMC material includes first fibers, a matrix, and at least one coefficient of thermal expansion (CTE) increasing additive. The first fibers include a first material having a first CTE value. The matrix includes a second material having a second CTE value. The at least one CTE increasing additive has a third CTE value. The EBC is disposed on at least one exposed surface of the CMC material and has a fourth CTE value. The third CTE value is greater than the first CTE value and the second CTE value, and the at least one CTE increasing additive is present within the CMC material in an amount that elevates a CTE value of the CMC material above the first CTE value or the second CTE value.

This application is a divisional of U.S. patent application Ser. No.16/240,062 filed Jan. 4, 2019, which is hereby incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION 1. Technical Field

The present disclosure relates to methods for producing ceramic matrixcomposites (“CMCs”) in general, and CMCs with modified thermal expansioncharacteristics in particular.

2. Background Information

Ceramic matrix composites (“CMC”) material may be utilized to form avariety of different components, and have particular utility in hightemperature environments such as within a gas turbine engine.

The low density and high temperature operating capabilities of CMCmaterials can be advantageous in many applications, including but notlimited to applications within gas turbine engines. Some CMCs, however,are susceptible to degradation (e.g., oxidation, etc.) in hightemperature environments; e.g., an environment such as that found in acombustor section and/or turbine section of a gas turbine engine. Inorder to protect the CMC, it is known to apply an environment barriercoating (“EBC”) to the exposed surfaces of the CMC component. In someinstances, the durability of an EBC applied to a CMC component may beaffected by differences in the coefficient of thermal expansion (“CTE”)between the EBC coating and the CMC substrate to which it is applied. Ifthe differences in the CTE of the EBC coating and the CTE of the CMCsubstrate are great enough, and the coated substrate is heated to asufficient temperature, the aforesaid CTE difference can result inmechanical deficit (e.g., cracks, etc.) in the EBC coating. Theaforesaid mechanical deficit can negatively affect the durability of theEBC coating. Silicon carbide (“SiC”), for example, is often presentwithin a CMC, and SiC often has a lower CTE than many EBCs. Hence, theremay be a CTE disparity there between that negatively affects thedurability of the CMC component. Indeed, in some instances, if there isa substantial CTE disparity or mismatch between the CTE of a CMCmaterial and the CTE of an EBC coating, a person of skill in the artwill recognize that the aforesaid EBC coating may not be considered as aviable EBC candidate for the CMC material for a given application. As aresult, in some applications there may be a limited number of EBCcoating materials available for use with a given CMC material, andconsequently that particular CMC material (and similar CMCs) may not bea viable candidate for certain component applications.

The problem caused by CTE mismatch is known in the prior art; e.g., thefailure of ZrO₂—Y₂O₃ EBCs due to the high CTE of the ZrO₂—Y₂O₃mismatched with SiC/SiC CMCs, resulting in cracking. (See Zhu, D., Lee,K. N. and Miller, R. A., 2002, January; “Thermal gradient cyclicbehavior of a thermal/environmental barrier coating system on SiC/SiCceramic matrix composites”; ASME Turbo Expo 2002: Power for Land, Sea,and Air (pp. 171-178), American Society of Mechanical Engineers). Asanother example, the prior art discloses cracking of an EBC comprisingytterbium monosilicate (Yb₂SiO₅) due to a CTE mismatch with SiC. (SeeRichards, Bradley T., Matthew R. Begley, and Haydn N G Wadley,“Mechanisms of ytterbium monosilicate/mullite/silicon coating failureduring thermal cycling in water vapor.” Journal of the American CeramicSociety 98, no. 12 (2015): 4066-4075)

What is needed, therefore, is a CMC that has an improved ability to beprotected by one or more different types of EBC coatings.

SUMMARY

A ceramic matrix composite (CMC) material component is provided thatincludes a CMC material and an environmental barrier coating (EBC). TheCMC material includes a plurality of first fibers, a matrix, and atleast one coefficient of thermal expansion (CTE) increasing additive.The plurality of first fibers includes a first material having a firstCTE value. The matrix is incorporated with the plurality of fibers. Thematrix includes a second material having a second CTE value. The atleast one CTE increasing additive has a third CTE value. The EBC isdisposed on at least one exposed surface of the CMC material. The EBChas a fourth CTE value. The third CTE value is greater than the firstCTE value and the second CTE value, and the at least one CTE increasingadditive is present within the CMC material in an amount that elevates aCTE value of the CMC material above the first CTE value or the secondCTE value.

According to another aspect of the present disclosure, a method ofproducing a ceramic matrix material (CMC) component is provided. Themethod includes producing a CMC material, including: a) providing aplurality of first fibers comprising a first material, the firstmaterial having a first coefficient of thermal expansion (CTE) value; b)incorporating a matrix with the plurality of first fibers, the matrixcomprising a second material having a second CTE value; and c)incorporating at least one CTE increasing additive having a third CTEvalue; and disposing an environmental barrier coating (EBC) on at leastone exposed surface of the CMC material, the EBC having a fourth CTEvalue. The third CTE value is greater than the first CTE value and thesecond CTE value, and the CTE increasing additive is present within theCMC in an amount that elevates a CTE value of the CMC above the firstCTE value or the second CTE value.

In any of the aspects or embodiments described above and herein, atleast one CTE increasing additive may be incorporated into the pluralityof fibers.

In any of the aspects or embodiments described above and herein, atleast one CTE increasing additive may be provided as fibers, and the CTEincreasing additive fibers may be incorporated with the first fibers toproduce a plurality of fiber tows and are incorporated into the CMC.

In any of the aspects or embodiments described above and herein, atleast one CTE increasing additive fibers may be a first CTE increasingadditive, and the at least one CTE increasing additive may include asecond CTE increasing additive that is incorporated into the matrix.

In any of the aspects or embodiments described above and herein, thesecond CTE increasing additive may be incorporated into the matrix inparticulate form.

In any of the aspects or embodiments described above and herein, the atleast one CTE increasing additive may be incorporated into the matrix.

In any of the aspects or embodiments described above and herein, thefirst CTE increasing additive may be incorporated into the matrix inparticulate form.

In any of the aspects or embodiments described above and herein, atleast one CTE increasing additive may include a first CTE increasingadditive in particulate form and a second CTE increasing additive infiber form.

In any of the aspects or embodiments described above and herein, thefirst material and the second material may be the same materials, andthe first CTE value equals the second CTE value.

In any of the aspects or embodiments described above and herein, thefirst material may be SiC, the at least one CTE increasing additive mayinclude at least one of Al₂O₃, ZrO₂—Y₂O₃, or MoSi₂, and the EBC may be arare-earth monosilicate.

In any of the aspects or embodiments described above or herein, thefourth CTE value and the CTE value of the CMC material may besufficiently close to one another such that the EBC isthermo-mechanically stable on the at least one exposed surface of theCMC material.

In any of the aspects or embodiments described above or herein, thefourth CTE value may be equal to or greater than the CTE value of theCMC material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of a ceramic matrix compositepreform.

FIG. 2 is a graph illustrating CTE values on the vertical axis, andmatrix filler volume fraction on the horizontal axis.

DETAILED DESCRIPTION

The present disclosure is directed to methods of increasing thecoefficient of thermal expansion (CTE) of a ceramic matrix composite(“CMC”) relative to an environmental barrier coating (“EBC”) applied toa surface of a substrate formed of the CMC material, and to CMCsubstrates or components having a CTE modified to more closely match theCTE of a respective EBC coating. A component or substrate formed with amodified CMC material according to the present disclosure (referred tohereinafter collectively as a “CMC component”) may have particularutility in high temperature applications (e.g., a gas turbine engine),but the present disclosure is not limited to a CMC component designedfor any particular application.

Referring to FIG. 1 , the manufacture of a CMC component typicallybegins with the production of a preform. The CMC preform may includefibers 10, but is not limited thereto. The fibers 10 may includediscontinuous fibers, continuous fibers, or some combination thereof.Each fiber 10 may be a fiber tow comprising a substantial number offilaments. The fibers 10 may be grouped into discrete bundles. Within aCMC preform, the fiber or fiber bundles (hereinafter collectivelyreferred to as the “fibers 10”) may be twisted or untwisted, and may bearranged in woven, non-woven, braided, knitted or other known fiberarchitectures. The CMC preform further includes a matrix 12 within whichthe fibers 10 reside.

The present disclosure is not limited to any particular manner ofcombining the fibers 10 and matrix 12 materials. As a non-limitingexample, a fiber architecture may be infiltrated with one or moreparticulate materials disposed within a liquid carrier; e.g., a slurry.The liquid mixture is applied to the fiber architecture in a manner thatallows for infiltration. The liquid carrier may be subsequently removed,leaving a deposit of the one or more particulate materials within thepreform. As will be discussed below, additional and/or differentinfiltration steps may be utilized to deposit additional materials inthe formation of the matrix. Other than inclusion of one or more aspectsdescribed herein, the present disclosure is not limited to anyparticular methodology for forming a CMC preform and the CMC componentproduced therefrom.

According to the present disclosure, a CMC material is modified with oneor more CTE increasing additives that change the CMC material into amodified CMC material having a CTE value that is greater than the CTEvalue of the original CMC material. The graph shown in FIG. 2 , forexample, illustrates the effect of adding zirconium oxide (“ZrO₂”) as aCTE increasing additive, or the effect of adding aluminum oxide(“Al₂O₃”) as a CTE increasing additive. The graph shown in FIG. 2includes CTE values (in units of ppmK⁻¹) on the vertical axis, andmatrix filler volume fraction on the horizontal axis. For descriptionsake, it may be assumed that the original CMC material has a first CTEvalue (“CTE1”), the modified CMC material has a second CTE value(“CTE2”), and an EBC coating that is for application to an exposedsurface of a CMC component has a third CTE value (“CTE3”), whereinCTE1<CTE2≤CTE3. CTE values, as used herein, may be described in terms ofthermal expansion per degree temperature. For example, CTE values may beexpressed in units of “ppm/K” or “ppmK⁻¹”, wherein the thermal expansionis identified in terms of “parts per million” or “ppm”, and thetemperature is identified in terms of degrees Kelvin. Other unitsrepresenting thermal expansion and temperature may be usedalternatively; e.g., “ppm/C”, “ppm/F”, etc.

The one or more CTE increasing additives that are added to the originalCMC material to form the modified CMC material, are added in a quantitythat is adequate to produce a modified CMC material with a CTE value(e.g., CTE2) that is sufficiently close to the CTE value of the EBCcoating (e.g., CTE3), such that the EBC coating bonded to the modifiedCMC material (e.g., bonded to a surface of a component comprising themodified CMC material) is thermo-mechanically stable on the modified CMCmaterial within a given set of environmental parameters. The term“thermo-mechanically stable” is used herein to describe applicationswherein the EBC coating on the modified CMC material acquires no morethan an acceptable amount of mechanical deficit (e.g., cracks, etc.)under predetermined environmental conditions (e.g., temperature, etc.)for a predetermined period of time; e.g., the application parameters ofa component comprising the modified CMC material. In other words, theamount of thermally induced cracking within the EBC coating, if any, isless than an amount that would prevent the modified CMC materialcomponent from being used in the aforesaid environmental conditions forthe predetermined period of time.

In embodiments of the present disclosure, a modified CMC material isprovided that has a CTE value that is substantially equal to the CTEvalue of the EBC coating that is to be applied to a component comprisingthe modified CMC material for a given set of environmental parameters.The relative equality between the modified CMC CTE value and the EBC CTEvalue for the given operating parameters may substantially decrease oreliminate mechanical deficit (e.g., cracks, etc.) that may be induced bythermal stress. In some instances, a CMC material modified according tothe present disclosure may make it possible to utilize an EBC coatingthat would not have been acceptable for use with the CMC material inunmodified form for a given set of environmental parameters.

Each CTE increasing additive should be thermodynamically stable with theother materials that are present within the unmodified CMC material. Inpreferred embodiments, the CTE increasing additive should also possessacceptable thermal conductivity, creep resistance, and toughness.

Each CTE increasing additive (which may also be referred to as “secondphase material”) typically has a CTE value that is higher than the CTEvalue of other materials within an unmodified version of the CMCmaterial. The addition of the one or more CTE increasing additivestherefore modifies the CMC material to have a higher CTE value than itwould otherwise. Each CTE increasing additive also typically has a CTEvalue that does not substantially exceed the CTE value of othermaterials within an unmodified version of the CMC material. In otherwords, the one or more CTE increasing additives do not possess a CTEvalue so high relative to the CTE value of the unmodified CMC material(e.g., the constituents therein) that the disparity between theaforesaid CTE values would create stress under operating parameters thatcould result in mechanical deficit. As an example, if the unmodified CMCmaterial is a SiC composition (which has a CTE value of approximately 5ppmK⁻¹), the one or more CTE increasing additives should each have a CTEvalue of at least about five ppmK⁻¹ (˜5 ppmK⁻¹), and should each have aCTE value of no more than about fifteen ppmK⁻¹ (˜15 ppmK⁻¹). These CTEvalues are non-limiting examples intended to illustrate relationship ofCTE values, and the present disclosure is not limited thereto.

A CTE increasing material may be incorporated into a CMC material toproduce a modified CMC material in a variety of different ways, orcombinations thereof. For example, in some embodiments a CTE increasingadditive may be incorporated into or added to the filaments that areused to form a fiber used in the CMC material. As another example, insome embodiments a CTE increasing additive may be incorporated into oradded to the fibers that are used to form a fiber bundle used in the CMCmaterial, or incorporated into or added to the bundle itself. As anotherexample, in some embodiments a CTE increasing additive may beincorporated into or added to the fibers or fiber bundles subsequent tothose fibers or fiber bundles being formed into a fiber architecture. Asanother example, in some embodiments a CTE increasing additive may beincorporated into or added to the matrix portion of the CMC material. Insome embodiments, including one or more of those described heretofore, aCTE increasing additive may be incorporated into or added to a CMCpreform (or portions thereof) by a deposition process such as chemicalvapor infiltration (“CVI”), or atomic layer deposition (“ALD”), or thelike. The inclusion of a CTE additive increasing additive may beperformed in multiple process steps, which process steps are similar ordifferent.

The present disclosure may be utilized with a variety of different typesof CMC materials; e.g. Carbon (“C”) fiber/C matrix, C fiber/SiC matrix,SiC fiber/Carbon matrix, SiC fiber/SiC matrix, Al₂O₃/Al₂O₃, etc. Thepresent disclosure is not limited to any particular CMC material,although it has particular utility for SiC based CMC materials due tothe typical CTE value disparity between SiC based materials and EBCcoating materials desirable for use in high temperature applications.The non-limiting examples provided in Table 1 below illustrate SiC basedCMC materials with one or more CTE increasing additives included toprovide a modified CMC material with a higher CTE (all percentages onvolume % basis of the CMC material).

TABLE 1 Example CMC Matrix No. CMC fiber material CTE increasingadditive 1 40% SiC 30% SiC 30% Al₂O₃ particles fibers matrix 2 30% SiC40% SiC 20% Al₂O₃ particles fibers matrix 10% Al₂O₃ fibers 3 40% SiC 40%SiC 20% c-ZrO—10Y2O3 particles fibers matrix 4 30% SiC 40% SiC 10% Al₂O₃fibers fibers matrix 20% c-ZrO—10Y2O3 particles 5 30% SiC 40% SiC 10%MoSi₂ fibers fibers matrix 20% Al₂O₃ particlesThe following examples are provided as non-limiting examples toillustrate the utility of the present disclosure.

Example 1: SiC fibers (e.g., Hi-Nicalon Type S provided by NGS AdvancedFibers Co., Ltd.) may be used to create fiber tows. The specific numberof fibers in a tow may vary depending on characteristics of the desiredtow and/or characteristics of the CMC component being produced. As anexample, a number of SiC fibers (e.g., 500) may be aligned parallel tocreate each tow. The fiber tows may be woven into plies, and acollection of the plies may then be shaped into a skeletal preform of acomponent. The SiC fibers only fill a portion of the skeletal preform(e.g., about 40% of the preform volume), thereby leaving a remainder ofthe skeletal preform (e.g., about 60%) as void space within theperimeter of the preform. The skeletal preform of fibers may then becoated with a thin interface coating; e.g., an initial layer of boronnitride (e.g., 500 nm thick), and a subsequent coating of SiC (e.g.,1500 nm thick). An example of a process that can be used to form thecoating(s) is a chemical vapor deposition (“CVD”) process, but thepresent disclosure is not limited thereto. Subsequent to the coatingsbeing applied, an aqueous slurry with aluminum oxide (Al₂O₃) particlesmay be introduced into the skeletal preform. The aluminum oxide particlesize may be chosen based on characteristics of the skeletal fiberpreform (e.g., relative size of the fibers, component configuration ofthe skeletal preform, etc.) to enhance permeation of the slurry withinskeletal preform. In many instances, a slurry having particles with amaximum dimension of in the range of about one to fifty microns (˜1μm-50 μm) are acceptable. The aqueous slurry is applied to the skeletalpreform such that a percentage (e.g., 30%) of the total volume enclosedby the perimeter of the preform is filled by the particulate matter(e.g., Al₂O₃), but not all of the total volume. To fill the remainingvoid space of the now particle loaded preform, the aforesaid preform maybe subjected to another vapor deposition process (e.g., CVD) to fill theremaining void space with SiC. A preform prepared in the mannerdescribed above may then be subject to additional steps known in the artto form the intended CMC substrate or component.

In this Example 1, the resultant SiC—Al₂O₃ composite has a CTE value ofabout 5.5 ppm/K, which is an increase relative to a SiC composite thatwould have a CTE value of about 5 ppm/K. The increase in CTE provided bythe SiC—Al₂O₃ composite provides a better CTE match for an EBC with anouter layer of yttrium monosilicate (YSi₂O₅). The improvement in CTEmatching mitigates thermal expansion in many thermal environments thatwould likely have otherwise created a mechanical deficit for a similarSiC CMC with an EBC of (YSi₂O₅).

Example 2: In this example, SiC fibers and Al₂O₃ fibers may becollectively used to make fiber tows. As stated above, the specificnumber of fibers in a tow may vary depending on characteristics of thedesired tow and/or characteristics of the CMC component being produced.An SiC/Al₂O₃ tow may be formed that comprises 75% SiC fibers and 25%Al₂O₃ fibers; e.g., a 500 fiber SiC/Al₂O₃ tow using the aforesaid fiberpercentages would include approximately 375 SiC fibers and 125 Al₂O₃fibers. These SiC/Al₂O₃ tows may then be woven into plies. The processesdescribed above in Example 1 may then be used to produce the preparedpreform that then may be subjected to additional steps known in the artto form the intended CMC component. In this example, the amount of Al₂O₃particles applied to the preform by the aqueous slurry is influenced bythe volume fraction of Al₂O₃ present within the tows to achieve thetotal volume fraction of Al₂O₃ desired in the finished preform.

Example 3: In this example the processes described above in Example 1are repeated, with the following change. In the example, the aqueousslurry contains ZrO₂-10Y₂O₃ particles in place of the Al₂O₃ particlesdescribed above. Like above, the ZrO₂-10Y₂O₃ particle size may be chosenbased on characteristics of the skeletal fiber preform (e.g., relativesize of the fibers, component configuration of the skeletal preform,etc.) to enhance permeation of the slurry within skeletal preform. Theaqueous slurry with ZrO₂-10Y₂O₃ may be configured and applied so thatthe finished preform contains about 20% by volume of the ZrO₂-10Y₂O₃particles.

In this Example 3, the resultant SiC—ZrO₂ composite has a CTE value ofabout 6.0 ppm/K, which is an increase relative to a SiC matrix whichwould have a CTE value of about ppm/K. The increase in CTE provided bythe SiC—ZrO₂ composite provides a better CTE match for an EBC with anouter layer of hafnium oxide (HfO₂). The improvement in CTE matchingmitigates thermal expansion in many thermal environments that wouldlikely have otherwise created a mechanical deficit for a similar SiC CMCwith an EBC of (YSi₂O₅).

Example 4: In this example the processes described above in Example 2are repeated, with the following change. In the example, the aqueousslurry contains ZrO₂-10Y₂O₃ particles in place of the Al₂O₃ particlesdescribed above. Like above, the ZrO₂-10Y₂O₃ particle size may be chosenbased on characteristics of the skeletal fiber preform (e.g., relativesize of the fibers, component configuration of the skeletal preform,etc.) to enhance permeation of the slurry within skeletal preform. Theaqueous slurry with ZrO₂-10Y₂O₃ may be configured and applied so thatthe finished preform contains about 20% by volume of the ZrO₂-10Y₂O₃particles. The present disclosure is not limited to any specific amountof Y₂O₃ within ZrO₂—Y₂O₃ mixtures.

Example 5: In this example, the processes and materials of Example 2 arerepeated with the following change. MoSi₂ fibers (rather than Al₂O₃fibers) are combined with the SiC fibers to collectively produce thefiber tows. As stated above, the specific number of fibers in a tow mayvary depending on characteristics of the desired tow and/orcharacteristics of the CMC component being produced. A SiC/MoSi₂ tow maybe formed that comprises 75% SiC fibers and 25% MoSi₂ fibers.

In these non-limiting examples, all of the percentages are volumetricpercentages. The CTE increasing additives may be added by a variety ofdifferent methodologies; e.g., the CTE increasing additive(s) inparticulate form may be added via a deposition technique such aschemical vapor infiltration (“CVI”). The CTE increasing additive(s) maybe added in combination with or separate from the matrix materials.

The present disclosure is not limited to use with any particular EBCcoating. Non-limiting examples of EBC coatings having utility with Sibased CMC materials include rare-earth monosilicates such as Y₂SiO₅(yttrium monosilicate), Gd₂SiO₅ (gadolinium monosilicate), Er₂SiO₅(erbium monosilicate), Yb₂SiO₅ (ytterbium monosilicate), and Lu₂SiO₅(lutetium disilicate) and HfO₂ (hafnium oxide).

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural forms thereof unless thecontext clearly indicates otherwise. Unless otherwise indicated, allnumbers expressing conditions, concentrations, dimensions, and so forthused in the specification and claims are to be understood as beingmodified in all instances by the term “about”.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the variations of theinvention. Additionally, certain steps may be performed concurrently ina parallel process when possible, as well as performed sequentially.Therefore, the particular order of the steps set forth in thedescription should not be construed as a limitation.

While various embodiments of the present disclosure have been disclosed,it will be apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible within the scope of thepresent disclosure. For example, the present disclosure as describedherein includes several aspects and embodiments that include particularfeatures. Although these features may be described individually, it iswithin the scope of the present disclosure that some or all of thesefeatures may be combined with any one of the aspects and remain withinthe scope of the present disclosure. Accordingly, the present disclosureis not to be restricted except in light of the attached claims and theirequivalents.

What is claimed is:
 1. A method of producing a ceramic matrix material(CMC) component, comprising: producing a CMC material, including:providing a plurality of first fibers comprising a first material, thefirst material having a first coefficient of thermal expansion (CTE)value; incorporating a matrix with the plurality of first fibers, thematrix comprising a second material having a second CTE value;incorporating at least one CTE increasing additive having a third CTEvalue; and disposing an environmental barrier coating (EBC) on at leastone exposed surface of the CMC material, the EBC having a fourth CTEvalue; wherein the third CTE value is greater than the first CTE valueand the second CTE value, and the CTE increasing additive is presentwithin the CMC in an amount that elevates a CTE value of the CMC abovethe first CTE value or the second CTE value.
 2. The method of claim 1,wherein the at least one CTE increasing additive is incorporated intothe plurality of first fibers.
 3. The method of claim 1, wherein the atleast one CTE increasing additive is provided as fibers, and the CTEincreasing additive fibers are incorporated with the plurality of firstfibers to produce a plurality of fiber tows and are incorporated intothe CMC.
 4. The method of claim 3, wherein the at least one CTEincreasing additive fibers are a first CTE increasing additive, and theat least one CTE increasing additive includes a second CTE increasingadditive that is incorporated into the matrix.
 5. The method of claim 4,wherein the second CTE increasing additive is incorporated into thematrix in particulate form.
 6. The method of claim 1, wherein the atleast one CTE increasing additive is incorporated into the matrix. 7.The method of claim 6, wherein the first CTE increasing additive isincorporated into the matrix in particulate form.
 8. The method of claim1, wherein the fourth CTE value and the CTE value of the CMC materialare sufficiently close to one another such that the EBC isthermo-mechanically stable on the at least one exposed surface of theCMC material.
 9. The method of claim 1, wherein the fourth CTE value isequal to or greater than the CTE value of the CMC material.
 10. Themethod of claim 1, wherein the first material is SiC, the at least oneCTE increasing additive includes at least one of Al₂O₃, ZrO₂—Y₂O₃, orMoSi₂, and the EBC is a rare-earth monosilicate.
 11. The method of claim1, wherein the at least one CTE increasing additive comprises Al₂O₃. 12.The method of claim 1, wherein the at least one CTE increasing additivecomprises ZrO₂—Y₂O₃.
 13. The method of claim 1, wherein the at least oneCTE increasing additive comprises MoSi₂.
 14. A ceramic matrix composite(CMC) material component, comprising: a CMC material comprising: aplurality of first fibers comprising a first material, the firstmaterial having a first coefficient of thermal expansion (CTE) value; amatrix incorporated with the plurality of fibers, the matrix comprisinga second material having a second CTE value; at least one CTE increasingadditive having a third CTE value; and an environmental barrier coating(EBC) disposed on at least one exposed surface of the CMC material, theEBC having a fourth CTE value; wherein the third CTE value is greaterthan the first CTE value and the second CTE value, and the at least oneCTE increasing additive is present within the CMC material in an amountthat elevates a CTE value of the CMC material above the first CTE valueor the second CTE value.
 15. The CMC material component of claim 14,wherein the at least one CTE increasing additive comprises Al₂O₃. 16.The CMC material component of claim 14, wherein the at least one CTEincreasing additive comprises MoSi₂.
 17. The CMC material component ofclaim 14, wherein the first material comprises carbon fibers and thematrix is a carbon matrix.
 18. The CMC material component of claim 14,wherein the first material comprises carbon fibers and the matrix is aSiC matrix.
 19. The CMC material component of claim 14, wherein thefirst material comprises SiC fibers and the matrix is a carbon matrix.20. The CMC material component of claim 14, wherein the first materialcomprises Al₂O₃ and the matrix is an Al₂O₃ matrix.